Conventional vehicles are equipped with various kinds of electrical circuit devices with sensors implemented on them. One example of this type of device is a collision detection electrical circuit device having a G-sensor (acceleration sensor) for detecting collisions and vibrations in anticipation of inflating an airbag mounted in the passenger compartment of the vehicle. FIG. 5 depicts a conventional collision detection electrical circuit device 101 including a circuit unit 102 having a G-sensor, a metal bushing 103, a resin case 104, and a bolt 105. The metal bushing 103 helps fasten the resin case 104 to a designated surface of the vehicle body. The resin case 104 unifies the structure of the circuit unit 102 and the bushing 103. The bolt 105 attaches the device 101 to the vehicle body. The electrical circuit device 101 is fastened onto the designated surface of the vehicle via the bolt 105. A threaded portion 105a of the bolt 105 enters a bolt-hole 103a of the bushing 103, which is laid in the resin case 104. A signal wire (not shown) electrically connects the electrical circuit device 101 to an airbag control device. The signal wire transfers a G-detection signal from the G-sensor to the airbag control device. Furthermore, the conventional structure includes a steel protection plate or collision guard in front of the electrical circuit device 101 on a collision-prone side or front side of the vehicle. The collision guard protects the electrical circuit device 101 from dislocation upon impact of collision and/or to protect the resin case 104 from malfunctioning due to the impact of collision.
In the conventional structure of the collision protection device described above, it is necessary to have a space for the standing steel plate to attach to the designated surface of the vehicle. Providing for such space poses restrictions on the flexibility of positioning and installing the electrical circuit device 101.